Personal area networks, PANs, are short range networks, typically ranging anywhere from a few centimeters to several meters and used to link multiple devices to each other and into networks, often temporarily. PANs allow devices to access communication and digital data services available via other devices or via other networks, for example the internet. In a simple set up a group of devices may form a PAN with a central device which is coupled to the internet, thus allowing devices in the PAN to access internet services.
PANs are typically wireless in nature and can operate using any wireless technology including, but not limited to radio, Bluetooth, ZigBee, Z-Wave, infrared technologies and other technologies including Body Area Network and Wireless USB. However they can also use wired technology including USB and FireWire technologies.
Devices suitable for connection to a PAN include any computing device capable of coupling via a communication technology and includes, but is not limited to, computers, laptops, tablets, palmtops, handheld devices, mobile phones including smart phones, but also includes peripheral devices such as printers, scanners, household monitoring and control devices and any device capable of forming a network node.
Typically a wireless device in a PAN performs a single role and is present in one single physical network at a time in which it can either be set up as a master or slave device.
The occurrence of multiple wireless devices in a PAN requires use of a communication technology which allows the devices to communicate while reducing packet collision, which occurs if two or more devices attempt to transmit on the same frequency at the same time, and interference. One such method is frequency hopping spread spectrum technique (FHSS) which allows the devices in a PAN to hop from one frequency to another, spreading transmissions over available bandwidth. This also utilises bandwidth resources efficiently. A frequency hopping data link layer model implies that access to medium is performed according to a predefined channel hopping pattern, executed at a time interval specified by a slot duration
Individual networks have communication schemes which stop their own devices from colliding. However when two or more networks coexist in the same space they are not necessarily aware of each other's frequency hopping spectra and collision may still occur if two devices in two different networks hop to the same or similar frequency and attempt to transmit or receive signals.
US 2002/0075941 describes a system which averts frequency collision and interference between devices in multiple networks in which master devices broadcast FHSS data to each other and to a central controller which coordinates hopping patterns. An adaptive priority system is used to avoid collision between devices.
Generally, while a device may usually only join one network at a time it is possible for devices to be members of multiple PANs. Switching between roles and networks is possible but usually only after a full reconfiguration. This is more complex if a single media interface needs to cope with the requirements of two or more networks with different spread spectrum techniques.
However, a frequency hopping mechanism usually requires that the device starting a network, which may be a PAN Coordinator or master, performs advertising of network hopping pattern parameters, including channel hopping pattern, time slot duration, start of a slot, channel offset, and other parameters which allow participating devices to take part in the PAN. The other network participants, the end devices, or slaves, will scan the medium for a long enough period to receive the advertising packets and configure required MAC/PHY layer parameters necessary to follow the specified channel hopping. Even though participating devices may now take part in a PAN, when a device is part of two or more different PANs collision may still occur if both networks require it to transmit or receive at the same time, or on the same frequency.